The determination of proportions or densities of different body materials in body parts of humans or animals is of utmost importance to monitor, for instance, cancer risk in clinical drug trials, epidemiological studies, or routine screening. The measures of proportions or densities could be shown to be useful as markers to predict, for instance, breast cancer risk and possibly risk of disease recurrence or change in breast cancer risk.
To obtain these measures, techniques have been developed to maximize the radiographic contrast of tissue composition of a body part to better discriminate cancer risk. The X-ray energies, dose levels, and film/screen combinations are typically designed to maximize the radiographic tissue composition contrast. As an example, breast density was initially described using a semi-quantitative classification system that took into account the quantitative (amount of density) and qualitative nature of the density (diffuse or associated with ductal structures). Four to ten category systems have been previously used to cover the entire density range. A more quantitative approach measures the area of mammographically dense breast area relative to the total projected breast area, referred to as mammographic density. Mammographic density is a quantitative continuous grading from 0 to 100% density measured by delineating the radiographically dense areas in the mammogram from the entire breast area and providing a percentage breast density. Although mammographic density is currently a widely used technique, it has serious limitations. First, since the films are uncalibrated for mass density versus film optical density, a unique threshold has to be picked for each film. Second, the total and dense projected areas will change based on the amount of compression. For example, in a typical laboratory, the reproducibility of delineating the dense regions by an expert radiologist on the same image is approximately 5-7%. If both delineation errors and patient repositioning errors are conservatively assumed to be 7%, the 95% confidence for a significant change in density is approximately 14%. Thus, the sensitivity for risk classification and change in follow-up examinations is similar to that of the categorical methods.
Accurate measurement of compressed breast thickness is an important factor in determining breast density. However, the measurement of actual thickness provided by commercial mammography systems can be as much as one centimeter off the actual thickness due to deflection of the breast compression plate.
Accordingly there is a need in the art to develop a device and method to quantify proportions or densities of different body materials in body parts of humans and animals that can more accurately determine the thickness of the body part under investigation.